1. Field
The present application generally relates to providing access to living body tissue, and in particular, to medical access devices provide access to living body tissue, including blood vessels.
2. Description of the Related Art
Many medical procedures require percutaneous placement of an interventional medical device, such as a catheter, into a body lumen such as an artery or vein. Such interventional medical devices may be used for, among other things, blood pressure monitoring, blood sampling, establishing access for a diagnostic and/or interventional procedure, and administering fluids and medicaments to a patient. In one aspect, percutaneous access to a patient's central venous system is an important aspect of administering intravenous therapy. It is desirable that the therapy be administered in the superior vena cava of the central venous system. In order to gain access, introducer devices are commonly used, through which other medical devices, such as a central venous catheter (CVC), are inserted. One such example of a CVC is a peripherally inserted central catheter (PICC). A PICC typically has one or more tubes, which are externally accessible by a clinician, that converge into a single catheter body that is internally implanted in a vein of the patient. The tubes are adapted to receive medicaments, which are then released through a distal tip of the catheter body into the central venous system of the patient.
In general, percutaneous techniques involve placing a needle through the skin and into a blood vessel, such as an artery or vein, until bleedback is achieved. This is followed by introduction of a flexible introducer guidewire to define the pathway through the skin and into the passageway or lumen of the blood vessel. The needle is then exchanged for an introducer sheath with dilator, which are concentric tubes that are advanced over the introducer guidewire and into the blood vessel. The introducer guidewire and dilator are removed, and exchanged for a catheter or other medical device to be used to deliver medication, and/or implantation of a medical implant such as a filter or a stent into the blood vessel through the introducer sheath.
The purpose of an introducer set is to place a section of tubing, for example an introducer sheath for a catheter, into a vessel, or other body part, that has a sufficiently large and rigid inner diameter to facilitate insertion of other proportionately large tubes, catheters, or other instruments into said vessel or body part. An introducer set commonly contains a small diameter device with a sharp tip, commonly a hypodermic needle, so that the introduction can start with a relatively small, easily produced, puncture wound, minimizing trauma to the involved tissues. This small puncture wound is then expanded, ideally by stretching rather than tearing or cutting the involved tissues, with a tapered dilator. The wall thickness of the introducer sheath is in some embodiments as small as possible, minimizing the outside diameter of the introducer sheath to minimize the trauma to the body tissues involved while maximizing the size of the inside of the opening for insertion of other devices.
Described is a procedure for preparing an opening to introduce devices into a blood vessel, a body opening, or other body duct is a multi-step procedure involving a number of independent devices and steps. The following steps set forth a conventional introducer set and method of use.
First, a hypodermic needle with glass or clear or translucent plastic syringe attached, is inserted into a vessel. When the pressure in the syringe is lower than the pressure in the vessel, blood will flow up the needle and into the syringe where it can be observed by the operator. Observed features, such as color and rate of flow of blood, confirm that a blood vessel has been hit, and indicate the type of vessel. The ability to observe the blood is a necessary part of the procedure for blood vessel access or, for example, access to a cyst or duct.
Second, while holding the needle in place, the syringe is disconnected from the needle. At this point, blood can flow, or squirt, out of the proximal opening of the needle and/or air can be sucked into the needle if the pressure in the body vessel should fall below ambient pressure. This latter effect can occur in a vein during normal inspiration, when the veins often collapse under negative pressure created in the venous system by the depression of the diaphragm.
Third, as quickly as possible, to minimize the above effects, a guidewire is inserted into the proximal end of the needle, effectively and approximately closing the hole and stopping fluid or air flow. The guidewire is then threaded well into the vessel. The guidewire is flexible to turn the corner from the needle-stick track, which enters the vessel at an acute angle.
Fourth, the needle is then removed by pulling the needle backwards over the full length of the guidewire while simultaneously holding the guidewire in place.
Fifth, a dilator with an introducer sheath slidingly positioned over the dilator is threaded onto the proximal end of the guidewire. The distal tip of the dilator has an inner diameter just large enough to slip over the guidewire with little friction. The outer diameter of the distal tip of the dilator is only slightly larger than the inner diameter, creating a relatively smooth transition from guidewire to dilator. The outer diameter of the dilator is tapered to a larger dimension, the taper occurring over a distance of about, for example, one or more centimeters back from the tip. The distal tip of the introducer sheath is positioned just proximal to the proximal end of the taper. As the dilator-sheath combination is pushed forward, the tip follows the guidewire into the vessel, and the following tapered outer dimension dilates the hole through the body and the wall of the vessel, stretching the inner diameter of the vessel to a larger than normal diameter. The dilator must also be flexible enough to turn the corner from the needle track to the long axis of the vessel. However, a relatively large force may be required to push the dilator through all the intervening tissues and to expand the vessel diameter, so the dilator/guidewire combination should have a proportionately large stiffness to prevent buckling. The distal end of the introducer sheath follows the dilator into the vessel. This sheath commonly has a constant inner diameter, just big enough to slip over the outer diameter of the dilator, and a constant-thickness thin wall. It should be flexible enough to pass from the body tissues outside the vessel, enter the vessel at an angle, and turn the corner to follow the long axis of the vessel. The force required again may be relatively large, but the dilator prevents buckling of the thin-walled, relatively flexible introducer sheath. Note that it could be difficult to insert the introducer sheath over the guidewire without inserting the dilator first because the required force would be great, the trauma to the tissues would be severe, and the stiffness of such a sheath would be inconsistent with the need for a flexible thin-walled device. Similarly, the size of the guidewire should be taken into consideration depending on the size of the sheath being introduced.
Sixth, the dilator is then withdrawn, holding only the introducer sheath, and perhaps the guidewire, in place. The guidewire can be removed as well. In some cases, the guidewire can be optionally exchanged for a second, larger diameter, stiffer guidewire, and the introducer sheath can be removed. A larger diameter dilator can then be inserted to enlarge the percutaneous opening, and then removed. A larger diameter introducer sheath and/or catheter (e.g., a dialysis catheter) can then be inserted. This introducer sheath permits repeated insertion and removal of useful devices of relatively large diameter, such as infusion catheters, balloon angioplasty catheters, angioscopes, etc. into the body and through the vessel wall without repeated trauma to vessel or intervening tissues. Improved methods and devices of accessing a body lumen are needed.